Heparin (HP) and heparan sulfate (HS) participate in a wide variety of physiological and pathological events, including viral infection, blood coagulation, cell differentiation and cancer metastasis. Their multi-faceted biological activities suggest that there are tremendous potential in using HP/HS as novel therapeutics. However, access to structurally well defined HP/HS oligosaccharides has been very difficult, which severely hinders the establishment of detailed structure activity relationships. In this application, a new synthetic strategy based on chemoenzymatic methods is proposed to acquire a panel of structurally diverse, precisely designed HP/HS oligosaccharides. In aim 1, chemical synthesis of HP/HS oligosaccharides using the pre-activation based one pot glycosylation method will be studied. The target structures will be systematically varied to include both glucuronic acid and iduronic acid in the backbone, diversified O-sulfation patterns, and differentiated nitrogen modifications. Oligosaccharides with sizes approaching those of polysaccharides will also be assembled. The pre-activation based one pot glycosylation method is highly advantageous as it allows rapid synthesis of HP/HS oligosaccharides with great sequence diversity. In aim 2, chemical synthesis will be integrated with enzymatic modification. The chemically prepared HP/HS oligosaccharides will be modified by sulfo transferases in a divergent manner, thus further increasing their sequence diversity. Moreover, glycosyl transferases will be used to elongate the functionalized HP/HS oligosaccharides, providing access to oligosaccharides composed of distinct domains. In aim 3, the precisely designed HP/HS oligosaccharides will be assayed for their heparanase inhibitory activities as well as growth factor and platelet factor 4 binding. The effects of backbone sequence, nitrogen substitution and O-sulfation will be evaluated to develop a highly specific heparanase inhibitor with low undesired biological interactions. The results of the proposed studies will establish the basis and tools for the structure-function relationship studies of HP/HS, leading to exciting opportunities for discovery of HP/HS based novel therapeutic agents.